• Journal of Korea Foundry Society
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• v.31 no.3
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• pp.145-151
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• 2011

Metallic foam has been known as a functional material which can be used for absorption properties of energy and sound. The unique characteristics of Al foam of mechanical, acoustic, thermal properties depend on density, cell size distribution and cell size, and these characteristics expected to apply industry field. Al-Zn-Mg-Cu alloy foams was fabricated by following process; firstly melting the Al alloy, thickening process of addition of Ca granule to increased of viscosity, foaming process of addition of titanium hydride powder to make the pores, holding in the furnace to form of cooling down to the room temperature. Metal foams with various porosity level were manufactured by change the foaming temperature. Compressive strength of the Al alloy foams was 2 times higher at 88% porosity and 1.2 times higher at 92% porosity than pure Al foams. It's sound and vibration absorption coefficient were higher than pure Al foams and with increasing porosity.

• Korean Journal of Materials Research
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• v.30 no.10
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• pp.542-549
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• 2020

Effects of Sc addition on microstructure, electrical conductivity, thermal conductivity and mechanical properties of the as-cast and as-extruded Al-2Zn-1Cu-0.3Mg-xSc (x = 0, 0.25, 0.5 wt%) alloys are investigated. The average grain size of the as-cast Al-2Zn-1Cu-0.3Mg alloy is 2,334 ㎛; however, this value drops to 914 and 529 ㎛ with addition of Sc element at 0.25 wt% and 0.5 wt%, respectively. This grain refinement is due to primary Al₃Sc phase forming during solidification. The as-extruded Al-2Zn-1Cu-0.3Mg alloy has a recrystallization structure consisting of almost equiaxed grains. However, the as-extruded Sc-containing alloys consist of grains that are extremely elongated in the extrusion direction. In addition, it is found that the proportion of low-angle grain boundaries below 15 degree is dominant. This is because the addition of Sc results in the formation of coherent and nano-scale Al₃Sc phases during hot extrusion, inhibiting the process of recrystallization and improving the strength by pinning of dislocations and the formation of subgrain boundaries. The maximum values of the yield and tensile strength are 126 MPa and 215 MPa for the as-extruded Al-2Zn-1Cu-0.3Mg-0.25Sc alloy, respectively. The increase in strength is probably due to the existence of nano-scale Al₃Sc precipitates and dense Al₂Cu phases. Thermal conductivity of the as-cast Al-2Zn-1Cu-0.3Mg-xSc alloy is reduced to 204, 187 and 183 W/MK by additions of elemental Sc of 0, 0.25 and 0.5 wt%, respectively. On the other hand, the thermal conductivity of the as-extruded Al-2Zn-1Cu-0.3Mg-xSc alloy is about 200 W/Mk regardless of the content of Sc. This is because of the formation of coherent Al₃Sc phase, which decreases Sc content and causes extremely high electrical resistivity.

• Journal of the Korean institute of surface engineering
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• v.41 no.3
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• pp.109-113
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• 2008

High strength 7xxx series Al-Zn-Mg alloy have been investigated for using light weight automotive parts especially for bump back beam. The composition of commercial 7xxx aluminum has the Zn/Mg ratio about 3 and Cu over 2 wt%, but this composition isn't adequate for appling to automotive bump back beam due to its high resistance to extrusion and bad weldability. In this study the Zn/Mg ratio was increased for better extrusion and Cu content was reduced for better welding. With this new composition we investigated the effect of composition on the resistivity against stress corrosion cracking. As the Zn/Mg ratio is increased fracture energy obtained by slow strain rate test was decreased, which means degradation of SCC resistance. While the fracture energy was increased with Cu contents although it is below 1%, which means improvement of SCC resistance. These effects of composition change on the SCC resistivity were identified by observing the fracture surface and crack propagation.

• Korean Journal of Materials Research
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• v.13 no.12
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• pp.819-824
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• 2003

The Al-7.7Zn-2.0Mg-1.9Cu-0.1Zr-0.1Sc alloy exhibited excellent elongation by the new thermomechanical treatment (TMT) process; solution treatment and furnace cooling\longrightarrowhot and cold rolling and then annealing for short time. Tensile test at high temperature from 430 to $500^{\circ}C$ has been performed with various strain rates using for the Al-7.7Zn-2.0Mg-1.9Cu-0.1Zr-0.1Sc alloy obtained by the TMT process. The elongation of the Al-7.7Zn-2.0Mg-1.9Cu-0.1Zr-0.1Sc was 550% tensile tested at $470^{\circ}C$ temperature and 2.2 $\times$ $10^{-3}$ $s^{-1}$ strain rate. The m value of Al-7.7Zn-2.0Mg-1.9Cu-0.1Zr-0.1Sc alloy deformed 85% increased from 0.33 to 0.46 with increasing total elongation. This new TMT process was very simple and easy to make the sheets in the company.

• Transactions of Materials Processing
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• v.29 no.3
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• pp.135-143
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• 2020

Low-cost alloying elements were added to a modified Al-6.5Si alloy and its microstructure, tensile and impact toughness properties were investigated. The alloying elements added were Mg, Zn, and Cu, and two kinds of alloy A (Mg:0.5, Zn:1, Cu:1.5 wt.%) and alloy B (Mg:2, Zn:1.5, Cu:2 wt.%) were prepared. In the as-cast Al-6.5Si alloys, Si phases were distributed at the dendrite interfaces, and Al₂Cu, Mg₂Si, Al₆ (Fe,Mn) and Al₅ (Fe,Mn)Si precipitates were also observed. The size and fraction of casting defects were measured to be higher for alloy A than for alloy B. The secondary dendrite arm spacing of alloy B was finer than that of alloy A. It was confirmed by the JMatPro S/W that the cooling rate of alloy B could be more rapid than alloy A. The alloy B had higher hardness and strength compared to the values of alloy A. However, the alloy A showed better impact toughness than alloy B. Based on the above results, the deformation mechanism of Al-6.5Si alloy and the improving method for mechanical properties were also discussed.

• Korean Journal of Metals and Materials
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• v.50 no.9
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• pp.669-675
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• 2012

Hot tearing was the most significant casting defect when the castability evaluation of the Al-Zn-Mg-Cu alloy system was conducted. It was related to the solidification range of the alloy. Therefore, the hot tear susceptibility of the AA7075 alloy, whose solidification range is the widest, was evaluated. The hot tear susceptibility was evaluated by using a mold for a hot tearing test designed to create the condition for the occurrence of hot tear in 8 steps. According to the tearing location and shape, a hot tear susceptibility index (HTS) score was measured. The solidification range of each alloy and hot tear susceptibility was compared and thereafter the microstructure of a near tear defect was observed. As a result, the HTS of the AA7075 alloy was found to be 67. Also, the HTS in relation to a change in Zn, Mg, Cu composition showed a difference of about 6-11% compared to the AA7075 alloy.

• Proceedings of the Materials Research Society of Korea Conference
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• 2002.05a
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• pp.86-86
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• 2002

• Proceedings of the Materials Research Society of Korea Conference
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• 2002.05a
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• pp.85-85
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• 2002

• Journal of Powder Materials
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• v.4 no.2
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• pp.100-105
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• 1997

In this study the changes of the hardness and microstructures during aging at 120$^{\cire}C$ of an RS-P/M Al-5.6wt%Zn-2.0wt%Mg-1.3wt%Zr-1.0wt%Mn-0.25wt%Cu alloy were studied using a transmission electron microscopy. The hardness increased rapidly at early stage of aging and reached the maximun when the specimen was aged for 24 hr. The many irregular-shaped $Al_4Mn$ and rod-shaped $Al_6Mn$ dispersoids with 0.1-0.4 $\mu$m in length were observed in the as-extruded alloy. The dark particles with 2-3 nm in size were observed in aged specimen for 5hr and those are thought to be G.P.zones or precursor of $\eta'$ precipitates. In aged specimen for 24 hr, the $\eta'$ phases were distributed homogeneously within the matrix and the PFZ with 30-40 nm in width was observed along the grain boundary. With further aging, the width of PFZ increased and $\eta$ phases were also detected within the matrix.

• Journal of Korea Foundry Society
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• v.35 no.4
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• pp.67-74
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• 2015

In this study, Mg-Zn alloys are investigated in terms of their thermal properties after an addition of Cu. Al element is added to improve the mechanical properties and castability in general case. However, it was excluded here because it significantly decreases the thermal conductivity. On the other hand, Zn was added as a major element, which had less influence on reducing the conductivity and can complement the mechanical properties as well. Cu was also added, and it improved the heat transfer characteristics as the amount was increased. The composition ranges of Zn and Cu are 6 wt.% and 0~1.5 wt.%, respectively. Mg-6Zn-xCu alloy was prepared by a gravity casting method using a steel mold and then the thermal conductivity and the microstructure of the as-cast material were investigated. By measuring the density_(${\rho}$), specific heat_(Cp) and thermal diffusivity_(${\alpha}$), the thermal conductivity_(${\lambda}$) was calculated by the equation ${\lambda}={\rho}{\cdot}Cp{\cdot}{\alpha}$. As the amount of Cu increased in the Mg-6Zn-xCu alloy, the heat transfer characteristics were improved, resulting in a synergistic effect which is slow when the added Cu exceeds 1 wt.%. In order to investigate the relative thermal conductivity/emission of the Mg-6Zn-xCu alloy, AZ91 and AZ31 were experimentally evaluated and compared using a separate test equipment. As a result, the Mg-6Zn-1.5Cu alloy when compared to AZ91 showed improvements in the thermal conductivity ranging from 30 to 60% with a nearly 20% improvement in the thermal emission.